1. Field of the Invention
This invention relates to the recovery of heat energy from geothermal aquifers.
2. Description of the Prior Art
The prior art pertinent to the present invention is believed to be limited to the technology which has been adapted to or developed in conjunction with recovery of thermal energy from geothermal brines.
The known art involved in the utilization of geothermal brines is summarized in number 12 of a series of publications by the Unesco Press on earth sciences; Geothermal Energy, Review of Research and Development (The Unesco Press, 7 Place de Fontenoy, 75700 Paris, France; (1973)).
Brines obtained from naturally heated aquifers have been utilized for various purposes since at least as early as ancient Rome. The most dramatic and best known use for geothermal energy is electric power generation, as practiced in Italy, Japan, Iceland, New Zealand, Mexico and the United States (California). In some locations, "dry" steam, produced as such from geothermal wells, is employed for this purpose. In other locations, wet steam, present as such in a geothermal formation or formed by flashing of hot brines, is used.
Most geothermal fluids, steam and hot water, contain dissolved non-condensible gases. Existing geothermal power processes utilizing hot water or brines often flash the fluid to produce motive steam which is then used in a steam turbine for production of electricity. The vast majority of the non-condensible gases present in the geothermal fluid are consequently flashed into the motive steam. The steam exhausting from the turbine is condensed under varying vacuum conditions. The non-condensible gases must be removed from the exhaust steam in order to maintain the desired vacuum in the turbine exhaust system. The equipment required to remove the non-condensibles can require a significant amount of power in the form of either motive steam for steam power ejectors, or mechanical power for vacuum pumps. Thermodynamic efficiency can be severely constrained as the percentage of non-condensible gases increases.
Some non-condensible gas components, such as hydrogen sulfide, are too obnoxious to be discharged to the atmosphere. Thus, when brines containing such gases are flashed to provide motive steam, the non-condensibles separated from the turbine exhaust cannot simply be vented to the atmosphere without additional treatment.
Pretreatment of geothermal brines or of steam produced therefrom has heretofore been limited to such practices as scrubbing of steam (at Wairakei, New Zealand) to remove entrained brine droplets. It has not previously been proposed to remove non-condensibles from hot waters or brines, otherwise suitable as sources of motive steam.